This invention relates to methods and an apparatus for the generation of a single-gear or multiple-gear grinding worm for grinding tooth profiles in accordance with the principle of continuous diagonal hob grinding.
The majority of the spur wheels used in gear technology today have involute tooth profiles. However, for power reasons the gearing of two involute toothed wheels often fails to produce an optimal operating response. Consequently, the tooth profiles are modified, divergent from the involute, by means of design calculations in the direction of both the depth and the width of the tooth. As the extent of such modifications generally falls within the micrometer range, grinding processes play a critical role in the generation of modified tooth profiles.
The more straightforward modifications of tooth profiles consist primarily of depth or width crowning, crown or root relief machining in relation to tooth depth, as well as end relief machining in relation to tooth width. If we view these modifications in terms of their change response in the two directions on a tooth profile (tooth depth and tooth width), we can see that they are tooth profile modifications that always change in only one tooth profile direction at a time, while remaining constant in the second tooth profile direction. During continuous hob grinding, these modifications can be achieved either by means of profiling of the grinding tool with special profiling tools (generally modifications in the direction of tooth depth) or by means of appropriate movement of the machine axes (generally modifications in the direction of tooth width). In the latter case, these additional axial movements during continuous hob grinding often result in unwanted distortion of the tooth face profile.
In contrast, the generation of complicated tooth face modifications is associated with various requirements in several face cuts and/or several cylinders. In extreme cases, each point on the face of the tooth may consist of a specific modification value (difference between the profile shape and the involute). The generation of this type of toothed wheel work by means of continuous hob grinding requires special technological procedures.
The technical status during the profiling of grinding worms remains an important factor in arriving at a solution. Referring to FIG. 1, a disk-shaped profiling tool 1 is often used in these types of procedures. This profiling tool is shifted in relation to a rotating grinding worm 2 by means of a lifting motion 3 in which the profiling tool touches the crown, the face and/or the root of one or both faces of the spiral 4. The lifting motion of the profiling tool and the rotational movement 5 of the grinding worm 2 are precisely attuned to one another, so that the profiling tool completes a path defined as P1 * module * number of starts within a single revolution of the worm. Of the multitude of procedural specifications applied in this regard, two general principles are known.
During profiling of the profile roll (FIG. 1a), the active section 6 of the disk-shaped profiling tool has a single-tapered or double-tapered profile. During the profiling procedure, this shape leads to a line contact between the profiling tool 1 and a normal section of the spiral 4. The advantage of these contact relationships is that the entire depth of the spiral (h), including the root and crown areas, can be profiled with a single lifting motion 3 of the profiling tool or of the grinding worm across the width of the grinding worm (bs). As an increasingly large section of the face depth of a spiral segment is engaged in this method (generally the entire profile), it will be referred to hereinafter as profile dressing.
Profiling with shaped rolls (FIG. 1b) involves the use of a disk-shaped profiling tool which may, for example, have a radius profile within the active section 6. In this tool, the contact between the profiling tool and the spiral is virtually punctiform. Thus, only a very limited section of the spiral depth (h) is profiled during each lifting motion 3 across the width of the grinding worm (b.sub.s). A multitude of profiling strokes is needed to profile the entire spiral, with the profiling tool being advanced by a defined value (.DELTA.U) along the spiral depth after each stroke. This profiling method leads to lengthy profiling times, particularly in the case of grinding worms with large modules. However, it is also known that, because of the point contact within the range of contact, this method is very advantageous for the generation of virtually infinite modifications along the spiral depth. In the following text, this method will be referred to as line-by-line profiling.
In a known procedure for generating complicated tooth face modifications in a hob grinding process, the grinding tool is tangentially displaced in relation to the toothed wheel during one cutting stroke (shifting or diagonal grinding) (DE 3704607). A special feature of the hob grinding procedure is that, because of the tangential shift taking place during the cutting stroke, a new contact line between the toothed wheel and the grinding worm can be allocated to each toothed wheel normal cut. Through the use of a grinding worm that has a spiral with continually changing face contact angles across its entire active width, the aforementioned procedure compensates for procedure-related distortion of the tooth face. This distortion occurs during the continuous hob grinding of diagonally toothed spur wheels if the axial distance between the workpiece and the tool changes during the cutting stroke (e.g., during the generation of crownings). A disadvantage of this procedure is that the grinding worm receives modified pressure angles (modifications) along its entire active width. Consequently, when grinding worms are used with conventional grinding agents, there is increased wear in those worm sections in which grinding is characterized by greater time-cutting volume. In contrast, more flexible profiling of the spiral with new pressure angle changes (modifications) is not possible when using a combination of grinding worms that cannot be profiled and super-hard grinding agents.
In regard to line-by-line profiling, a procedure is known (WO 95/24989) in which a grinding worm is given various modifications in various width sections, beginning with the tooth face modifications to be generated. During application of line-by-line profiling of the grinding worm, these individual width sections are given modifications along the depth of the spiral which differ from section to section but remain constant within a given section. As a result, there are transitional sections between the individual width sections of the grinding worm in which a transition occurs between the spiral depth modification of one width section and of the spiral depth modification of the following width section. The generation of continuous face modifications in the direction of worm width and, consequently, in the direction of tooth face width, is not possible with this procedure.